Sound-trapping muffler construction



' y 13,1948 c. STRACHAN SOUND-TRAPPING MUFFLER CONSTRUCTION s Sheets-Sheet 1 I Filed June 26, 1944 A ORNE July 13, 1948. c STRACHAN SOUND-TRAPPING MUFFLER CONSTRUCTION 3 Sheets-Sheet 2 Filed June 26, 1944 C. STRACHAN SOUND- TRAPPING MUFFLER CONSTRUCTION July 13, 1948.

3 Sheets-Sheet 3 Filed June 26, 1944 Patented July 13, 1948 UNITED STATES PATENT OFFICE SOUND-TRAPPING MUFFLER CONSTRUCTION 4 Claims.

My present invention relates generally to mufflers for internal combustion engines and the like.

A general object is to provide certain improvements in the design of a mufiler whereby a more effective silencing action can be obtained without any sacrifice in structural simplicity and compactness, ease of manufacture, or efficiency of operation. A muffler constructed in accordance with the present invention is not only measurably more effective in its silencing effect than the best commercially available mufflers of more conventional design and of comparable capacity, but in many cases achieves a silencing result which is at least as good as, if not better than, ordinary mufflers of larger size.

It is well known that the exhaust gases of an internal combustion engine emanate in the form of a columnar stream in which there are successive concentrations at relatively elevated pressures, with intermediate regions of relatively low pressure. It is this irregularity which produces the characteristic succession of explosive noises for whose elimination or reduction at mufller is employed; Generally speaking, it is a function of the muffler to level out the successive high-pressure and low-pressure impulses, and one wellestablished practice to accomplish this result lies in affording an opportunity ofthe high-pressure masses of gas to expand prior to the ultimate discharge of the exhaust gases from the muffler. For eflicient operation, the muffler should'accomplish its purpose without materially increasing the back-pressure on the engin and by means of a structure'which is as compact as possible.

Theplfesent improved design is predicated upon a full realization of the fact that the characteristicsoundof an engine exhaust is only partially due to the gas impulses referred to, another factor being the-noise within the engine itself, manitested in the form of sound waves traveling through the exhaust gases as the latter pass through-the mufiler. These sound Waves travel with considerably greater speed than the exhaust gases themselves, and emanate from the muffler even-whenthelatter is effectively leveling out the pressure impulses. In fact, regardless of any leveling of pressure variations, the column of exhaustgases serves continuously as a medium for thgtransmission of the sound Waves mentioned, so that even though a muffler may successfully iron out theexhaust gas impulses and thus silence the primary cause of undesired noise, it may nevertheless continue to transmit the sound waves emanating from the engine-itself unless special provision is made for their diminution.

In accordance with my present invention, this double objective is sought to be achieved in a single, compact, and relatively'simple'mufller'unit, by means of an arrangement of parts specifically designed to reduce the explosive-impulse noise factor mechanically, while simultaneously reducing the sound-wave factor by a treatment primarily acoustic in character. Thus, to disrupt the: successive pressure impulses, the exhaust gases are conducted through a relatively extended" path of travel of progressively increasing cross-sectional area; to diminish or dampen the faster-moving and more persistent sound Waves from the engine:

itself; one or more sound traps are provided whereby the sound waves are effectively attenuated during their transmission through the exhaust gas column.

The sound trap I'prefer to employ is a dead-end chamber in communication with the exhaust gas column through a plurality of laterally-disposed relatively small perforations, the term deadend as used herein and in the appended-claimsbeing intended to signify that it is extraneous toand forms no part of the fundamental path of travel of the exhaust gases from the inlet to: the

outlet of the mufiler; Where one such sound trap a substantially helical conduit formed in a substantially cylindrical mufiler shell, and the conduit is built up of a set of annular sections transversely arranged with respect to the muffler axis and in series communication. One simple and commercially-feasible manner of providing such a helical conduit lies in the special spaced arrangement of structurally simple transverse partitions anddeflectors hereinafter to be described. This construction lends itself admirably to the simultaneous accomplishment of the acoustic re-- sults which the improved muffler achieves.

In other embodiments of the invention, the extended path of travel of the exhaust gases is provided for by means of longitudinally-arranged partitions which define a conduit in which the flow is back and forth along longitudinal passes of progressively increasing cross-sectional area.

I achieve the foregoing general objectives, and such other objects and advantages as may here'- conduit inafter appear or be pointed out, in the manner illustratively exemplified in the accompanying drawings, in which:

Figure 1 is a longitudinal cross-sectional view of a muffler embodying the features of the present invention;

Figure 2 is a cross-sectional view taken substantially along the line 2-2 of Figure 1;

Figure 3 is a fragmentary perspective view of some of the partitions employed in the structure of Figure 1, showing a preferred arrangement of deflectors for defining a continuous helical conduit;

Figure 4 is a view similar to Figure 1 illustrating a modification;

Figure 5 is a cross-sectional view taken substantially along the line 5-5 of Figure 4, with parts broken away to reveal structure which would be otherwise hidden;

Figure 6 is a cross-sectional view taken substantially along the line 6-6 of Figure 4;

Figure '7 is a view similar to Figures 1 and 4, illustrating a second modification;

Figure 8 is a cross-sectional view taken substantially along the line 88 of Figure 7;

Figure 9 is a view similar to Figures 1, 4, and '7, illustrating a third modification, this view being taken substantially along the line 9-9 of Figure 10;

Figure 10 is a cross-sectional view taken substantially along the line Iii-I0 of Figure 9;

Figure 11 is a cross-sectional view taken substantially along the line of Figure 9; and

Figure 12 is a fragmentary perspective View, showing the arrangement of partitions employed in the structure of Figures 9-11.

In the muffler illustrated by way of example in Figures 1-3 a substantially cylindrical shell 20, of elongated character, is provided with an inlet 2| at one end and an outlet 22 at the other. In the region adjacent to the inlet there is a substantially cylindrical wall 23 of lesser length and diameter than the shell 20, defining an. annular chamber 24 around it.

Extending transversely across the mufiler are a series of spaced partitions. Any suitable or desired number of such partitions may be provided, :and I have illustratively shown a total of ten, designated successively by the reference numerals 25-34 inclusive. These partitions are mounted upon an axial core 35 which may be either solid or hollow. I have illustratively shown this core of hollow character whereby an axial chamber 36 is provided.

The partitions 25 and 34 extend across the ends of this core so that the chamber 36 becomes a dead-end chamber. The partitions 25-28 extend laterally to the wall 23, while the other partitions extend all the way to the shell 20. The partition 29 thus serves in its marginal portion to seal the end of the annular chamber 24, thereby making this chamber, also, a dead-end chamber.

Each of the partitions 25-34 has a radial aperture, and connecting baffles or deflectors are arranged between one edge of each aperture and the opposite edge of the aperture in the adjacent partition thus defining a substantially helical conduit through which exhaust gases entering at 2| are conducted as they travel through the mufiler from the inlet 2| to the outlet 22.

The structural nature of this substantially helical conduit is best illustrated in Figure 3 in which the partitions 25-29 have been shown in a fragmentary perspective view. It will be observed that the partition 25 has a radial aperture de- '4 fined by the opposite edges 31 and 38; the partition 28 has a. similar radial aperture defined by the edges 39 and 40; the partition 21 has a similar radial aperture defined by the edges 4| and 42; and the partition 28 has a radial aperture defined by the edges 43 and 44. The radial aperture in the partition 29 is of similar character except that it does not extend all the way to the peripheral edge of this partition but terminates at the curved edge 45. One of the side edges of this aperture is visible in Figure 3 and is designated 46, the other edge is concealed. The partitions are so arranged that each pair of edges 38-39, 40- 42-43, 44-46, and so on, are parallel. This per-- mits deflectors of plane upwarped character to be welded or otherwise secured into position as shown. Thus, the deflector 41 extends between the edges 38 and 39, a similar deflector 48 extends between the edges 40 and 4|, a similar deflector 49 extends between the edges 42 and 43, and so on.

As a result, the gases entering the muffler through the inlet 2| will pass through the aperture in the partition 25 and will be directed in a circumferential direction through the space between the partitions 25 and 26. Upon encountering the deflector 41 they will pass through the radial aperture in the partition 26 and will be directed by the deflector 48 into a similar circumi'erential travel through the space between the partitions 26 and 21. A similar circular travel occurs between each pair of transverse partitions, and ultimately the gases will pass outwardly through the radial aperture in the partition 34 (not shown) into the space 50 adjacent to the outlet 22. In this space, a conical deflector 5| is preferably provided so as to constrain the gases to a movement around the edge of this deflector before they pass into the outlet pipe 22.

It will be understood that the construction illustrated in Figure 3 is continued throughout the series of transverse partitions, and that each of the partitions 30-34 has a radial aperture similar to those shown in the partitions 25-28, i. e., the radial aperture in each case extends all the way to the peripheral edge of the partition in which it is formed.

In order that the helical conduit may have a progressively increasing cross-sectional area, the apertures in the various transverse partitions are of suitably chosen angularity. For example, the angle between the edges 43 and 44 is greater than the angle between the edges 4| and 42, the latter angle is in turn greater than the angle between the edges 39 and 40, and so on. Similarly, the transverse partitions are spaced at varying amounts. Thus, it will be observed in Figure 1, that the partitions 25-26 are closer together than the partitions 26-21, and so on. Of course, where the radial size of the partitions increases, the spacing between them may be correspondingly reduced. Thus, it will be observed that the partitions 29-30 are closer together than the preceding partitions 28-29, nevertheless the cross-sectional area of the conduit in the space between the partitions 29 and 30 is greater than the cross-sectional area of the conduit between the space of the partitions 29 and 29.

The increase in cross-sectional area of the conduit will depend upon the purpose to which the mufller is to be put, but in the illustrated construction, shown by way of example, a preferred relationship of parts is shown whereby the crosssectional area between the partitions 25 and 25 is one hundred per cent of the inlet area (i. e., the cross-sectional area of the inlet pipe 2|),

while the conduit area between the partitions 26 and 2-1 is one hundred twenty percent, the conduit area between the partitions 21 and 28 is one hundred forty per cent, and so on, each transverse circular section of the conduit increasing. in cross-sectional area by twenty per cent of the inlet area.

By virtue of this progressively increasing size of the conduit, the pressure impulses of the exhaust gases entering at 2i are given an extended opportunity to level out. That is to say, each concentration or plug of gas at relatively elevated pressure is given an opportunity to expand during. its passage through the muffler. In this way, when the gases leave through the outlet 22 they leave in the form of a stream which is at substantially uniform pressure. This serves to eliminate, or at least greatly minimize, the characteristic sound of successive explosions. I have found, however, that this treatment of the eX- haust gases does not by itself eliminate the more persistent, sound waves which are transmitted (through the stream of exhaust gases as a carrying medium) from the engine itself. To accomplish this latter and purely acoustic result, the present structure is characterized by the provision'of one or more sound-traps.

It will be observed that the wall 23 is provided. with a series of relatively small perforations 52 which establish a lateral communication between the narrower portion of the helical conduit and the annular space 24. The latter being a dead-end chamber, serves as a sound trap, and is particularly effective in eliminating sound waves of lower frequency. It is my belief that the communication established through the perforations 52' serves to progressively reduce the amplitude of the sound vibrations, dampening both the peaks and. the valleys of the sound waves as the latter are transmitted through the muffler. While it is true that a certain amount of gas will pass from the helical conduit into the dead-end chamber 24, and back again, I have found that this does not materially interfere with the main helical travel of the gases, nor is the helically-traveling gas'stream materially altered by any shortcircuiting or by-passing of gases by virtue of the provision of the perforations 52.

It will be understood that the dead-end cham ber 24 can be extended, if desired, for the full length of the mufller. It has been found, however, that an annular dead-end chamber, as shown at 24V in Figure 1, is admirably suited to serve as a sound trap for the elimination or material diminution of the objectionable sound waves.

For illustrative purposes, I have shown an additional series of relatively small perforations 53 in the wall 35 of the axial chamber 36. This permits the latter chamber to serve as an addi tional sound trap. Under certain circumstances, this may be desirable, although it is not essential. And although I have shown the perforations 53 arranged only in one part of the wall 35, it will be understood that similar perforations may be provided in other portions of this wall to enhance the sound dampening effect.

While the muffler may obviously be of any selected size, depending upon the use to which it is to be" put, the general nature of the invention may perhaps be better understood by stating that a muffler as shown in Figure 1 has produced an cellent results in connection with a four-cylinder Diesel engine having a continuous horsepowerof 25, an overload horsepower of 29, a

continuous speed of 1200. R. P. M. and an overload speed of 1500 R. P. M., where the inlet 2| of the mufiler is approximately 2" in diameter and the muffler as a whole is about 25" long and about 7%" in outside diameter. In an installation of the character described, the back pressure created by the muffler is only 11" of water, and the noise level (under overload conditions) measured 10 away from the outlet 22 and directly in front of the tail pipe is only decibels. Since a noise level of 91 or 92 decibels, measured in the same manner, has heretofore been considered indicative of satisfactory scund-muiiling characteristics, the added advantages achieved by the present construction will be obvious to those skilled in the art.

The sound trap or sound traps may be arranged in other relationships within the muffler, and it is not absolutely essential under all circumstances that the extended path of travel of the gases be helical in character. To illustrate the possible ramifications of my invention, I have shown various modified constructions in Figures 4-42.

Referring for the moment to Figures 4-6, I have shown an elongated shell 54 provided with an inlet 55 at one end of it, and an outlet -53 at the other end. Within the shell I provide a series of longitudinal partitions 5'l-64. They are arranged in superposed substantially parallel planes, and extend laterally to the shell 54 as indicated most clearly in Figures 5 and 6. They are of shorter longitudinal length than the shell, however, and cooperate with a pair of spaced transverse walls 65 and 6E. Alternate longitudinal partitions extend to the wall 65, not to the wall 66, and vice versa. Accordingly, an extended path of travel is provided, in the form of a conduit which communicates at 6'! with the inlet of the muffler and at 68 with the outlet, the conduit having adjacent longitudinal sections in series communication, whereby the gases travel back and forth along longitudinal paths indicated by the arrows in Figure 4.

Associated with the end wall 65 is a transverse wall 89 which is preferably inclined, as shown, and similarly associated with the wall 66 is a wall it. These walls are so arranged as to define dead-end chambers H and '52 respectively, each of these chambers being substantially transverse with respect to the muffler axis, and having substantially the shape of a segment of an orange. The wall 65 is provided with a series of rela tively small perforations it which establish communication between the conduit and the chamber H; and a similar set of perforations M is formed in the wall 66 to establish a similar communication with the dead-end chamber 12.

So far as the main travel of the gas stream is concerned, the perforations l3 and [4 are in lateral wall portions of the conduit, and establish a lateral communication which does not materially impair the main path of travel but which definitely serves to dampen and thereby eliminate the objectionable sound waves.

The longitudinal partitions 51-64 are so spaced from one another, with due regard to the contour of the shell 54 itself, that the successive conduit sections are of progressively increasing cross-sectional area. The conduit thus serves, as in the previous embodiment of the invention, to afford an opportunity for the high pressure masses of gas to expand during the passage of the gases through the mufiler. This eliminates or highly diminishes the primary cause of the characteristic engine exhaust noise. The sound traps H and 12 have an added acoustic eifect which further diminishes the totality of sound or noise emanating from the muffler.

In Figures 7 and 8 I have illustrated a further modification which is similar to that of Figure 6 except that the two transverse sound traps are in this case replaced by a single sound trap chamber 15 of annular shape. The muiller shell 16 is associated with an inner shell 11 which thus provides the annular chamber 75 around it. Longitudinal partitions 188l are associated with transverse end walls 82 and 83 within the confines of the inner shell 11, alternate longitudinal partitions extending to the wall 82 but not to the wall 83, and vice versa. This provides a conduit which communicates at 84 with the inlet 85 of the muilier and at 86 with the outlet 81 of the mufiler. The gases travel back and forth along adjacent longitudinal conduit sections, and the partitions l88l are so spaced (see Figure 8) that the cross-sectional area of the conduit progressively increases from the inlet to the outlet In this case, lateral communication is established between the conduit and the annular sound trap chamber 15 by means of a series of relatively small perforations 88 provided in the inner shell 11 In Figures 9-12 I have illustrated a further modification in which the longitudinal partitions are arranged in radial relationship instead of in parallel planes. In this case, as in Figure 7, the mufller is composed of an outer elongated shell 89 (having an inlet 90 at one end and an outlet 9! at the other) and an inner shell 92 is mounted so as to provide an annular dead-end chamber 93 around it. A pair of spaced transverse walls 94 and 95 extend across the inner shell, and mounted between these transverse walls are a series of longitudinal partitions 96-!90 (see Fig-- ures 11 and 12) arranged in radial relationship. Alternate partitions extend longitudinally to the transverse wall 94 but not to the wall 95, and vice versa, but all of the partitions extend radially to the shell 92. This provides a back and forth path of travel for the gases which is analogous to that of Figures 4. and 7. The wall 94 is provided with a radial aperture liil which permits the gases entering at 90 to pass into the angular space I03 (Figure 12) between the partitions 9S and 91. As the gases reach the wall 95, they are caused to turn back and travel through the angular space I04 (Figure 12) between the partitions 91 and 98, and so on. Ultimately, they pass through a suitable radial aperture I06 (Figure 11) in the wall 95 which communicates with the angular space I (Figure 9) between the partitions I09 and 96, and are thus permitted to leave the muiiier through the outlet 9|. The angles between the longitudinal partitions are of progressively increasing size, as shown most clearly in Figure 11, and the conduit thus has a progressively increasing cross-sectional area which permits the pressure impulses in the exhaust gases to become leveled out prior to the discharge of the gases from the muflier. The acoustic eifect which characterizes my present invention is produced in this case by a series of relatively small perforations I02 in the inner shell 92, establishing a lateral communication between the successive conduit sections and the dead-end chamber 93.

In each of the foregoing illustrative embodiments of the invention, the sizes of the perforations will depend upon the results desired and upon the cross-sectional area of the conduit and the type of engine which is being employed. By way of example, it may be stated that a muffler of the character shown in Figure 1 operates to best advantage when there are approximately eight A holes or perforations in each circumferential section of the conduit. Where the modified types of mufilers are of corresponding capacity, holes or perforations of similar or approximately similar dimensions are adequate to produce the desired effect.

In each of the constructions illustrated, the sound trap has been shown in the form or a deadend chamber which is completely closed, so far as the exterior of the muiller is concerned. This is not essential, and where the possible escape of exhaust gases in a lateral direction from such a sound. trap chamber is not objectionable or unieasible, a communication may be established between the sound trap chamber and the atmosphere without impairing its acoustic efiect. It is therefore to be understood that the term deadend as used herein and in the appended claims is intended to include within its significance a sound trapping chamber of such type, the term dead-em being primarily intended to signify the lateral disposition with respect to the main path of travel of the gases through the mufller, and of sufficiently enclosed character to leave the fundamental guidance of the gases through the mmiier unimpaired.

In general, it will be understood that the details herein described and illustrated may be modified in a number of respects by those skilled in the art without necessarily departing from the spirit and scope of the invention as expressed in the appended claims. It is therefore intended that these details be interpreted as being purely il1us trative, unless otherwise specifically pointed out.

Having thus described my invention and illustrated its use, what I claim as new and desire to secure by Letters Patent is:

1. In a muiiler for exhaust gases from an engine, a substantially cylindrical shell provided with an inlet at one end and an outlet at the other, and means in the shell for conducting the gases from the inlet to the outlet through a substantially helical path, said means comprising transversely-arranged partitions defining a set of annular sections in series communication, said sections being of progressively increasing crosssectional area, the sections in at least one longitudinal region of said set having a common outer wall which is substantially cylindrical and of lesser diameter than said shell, said wall being provided with a plurality of relatively small perforations communicating with the annular space between said wall and shell, said space being a dead-end chamber constituting a sound trap.

2. In a mufiler for exhaust gases from an engine, a substantially cylindrical shell provided with an inlet at one end and an outlet at the other, and means in the shell for conducting the gases from the inlet to the outlet through a substantially helical path, said means comprising transversely-arranged partitions defining a set of annular sections in series communication, said sections being of progressively increasing crosssectional area, certain adjacent sections in the inlet region of said set having a common outer wall which is substantially cylindrical and of lesser diameter than said shell, said wall being provided with a plurality of relatively small perforations communicating with the annular space thereof,

between said wall and shell, said space being a dead-end chamber constituting a sound trap.

3. In a muiiier for exhaust gases from an engine, a substantially cylindrical shell provided with an inlet at one end and an outlet at the other, and means in the shell for conducting the gases from the inlet to the outlet through a substantially helical path, said means comprising transversely-arranged partitions defining a set, of annular sections in series communication, said sections being of progressively increasing crosssectional area, the sections in at least one longitudinal region of said set having a common outer wall which is substantially cylindrical and of lesser diameter than said shell, said wall being provided with a plurality of relatively small perforations communicating with the annuar space between said wall and shell, said space being a dead-end chamber constituting a sound trap, said sections having also a common inner wall which is substantially cylindrical and definies an axiallyarranged chamber, said wall being provided with a plurality of relatively small perforations so that said axially-arranged chamber serves as another sound trap.

4. In a muffler for exhaust gases from an engine, a substantially cylindrical shell provided with an inlet at one end and an outlet at the other, a substantially cylindrical wall of lesser diameter and length concentrically arranged within said shell adjacent to the inlet region means for conducting gases from the inlet to the outlet through a substantially helical path, said means comprising an axially-arranged core and transversely-arranged partitions mounted on said core, the partitions within the confines of said wall terminating at said wall and the other partitions terminating at said shell, the margin of the partition at the inner end of said wall defining an end for the resultant annular deadend chamber between said wall and shell, each partition having a radial aperture, a deflector between each pair of partitions extending from one radial edge of One aperture to the opposite radial edge of the adjacent aperture, said partitions and deflectors thus defining a set of annular sections in series communication, said partitions being so spaced that said sections are of progressively increasing cross-sectional area from the inlet to the outlet, and a plurality of relatively small perforations in said cylindrical wall establishing a soundtrapping communication between said dead-end chamber and the sections which it surrounds.

CHRISTOPHER STRACHAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 825,010 Snow July 3, 1906 1,584,215 Clawson May 11, 1926 1,683,084 MaeKenzie et a1. Sept. 4, 1928 1,953,123 Oldberg et a1 Apr. 3, 1934 2,038,309 Oldberg Apr. 21, 1936 2,116,751 Deremer May 10, 1938 2,265,342 Bourne Dec. 9, 1941 2,359,365 Katcher Oct. 3, 1944 

